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A Cahn-Hilliard approach to modelling phase separation in bimetallic nanoparticles

Ahmed, Mohammad Afraz (2015)
Ph.D. thesis, University of Birmingham.

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Abstract

A ternary system of Cahn-Hilliard equations is used to model phase separation processes in bimetallic nanoparticles. The third component in the ternary system is taken to be vacuum, such that we are able to simulate bimetallic nanoparticles without any need to impose restrictions on the nanoparticle boundary. Strain effects, due to lattice mismatch, are introduced by coupling with the Navier-Lamé equations. The use of this diffuse-interface approach allows the simulation of significantly larger systems than currently feasible with atomistic methods. Particular attention is paid to the core-shell to quasi-Janus particle transition that has been observed in CuAg and other bimetallic nanoparticles of weakly miscible elements. Our simulations are able to capture the various effects seen previously in experimental work and in atomistic simulations. In particular, we observe a transition from core-shell structure to quasi-Janus particle structure as the size of the particles increases. Moreover, it is shown that core-shell particles prevail when the thickness of the shell is small in comparison to the core size. The inclusion of elastic effects into the model further promotes the formation of quasi-Janus particles. The transition from core-shell to quasi-Janus particle structure is, however, also seen in the absence of elastic effects.

Type of Work:Ph.D. thesis.
Supervisor(s):Warnken, Nils and Johnston, Roy (Professor)
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and Materials
Subjects:QC Physics
QD Chemistry
TP Chemical technology
Institution:University of Birmingham
ID Code:6284
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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